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Published on: October 10, 2025
Fibroblast growth factor 23 concentrations in healthy term infants during the early postpartum period
Masanori Takaiwa1, Kunihiko Aya, Takayuki Miyai
1Department of Pediatrics, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan. gmd13050@s.okayama-u.ac.jp
Insights
Fibroblast growth factor 23 (FGF23) is crucial for mineral balance. In newborns, FGF23 is fragmented, impacting phosphate homeostasis and potentially explaining early infant mineral metabolism changes.
Area of Science:
- Endocrinology
- Neonatal Physiology
- Mineral Metabolism
Background:
- Fibroblast growth factor 23 (FGF23) regulates phosphate (Pi) and vitamin D. Neonatal mineral metabolism shows distinct changes in calcium (Ca), Pi, parathyroid hormone (PTH), and vitamin D.
- The specific role of FGF23 in early neonatal mineral metabolism remains unclear.
Purpose of the Study:
- To investigate the significance of FGF23 in early postpartum mineral metabolism.
- To evaluate circulating FGF23 levels in umbilical cord blood and in infants at 5 days of life.
Main Methods:
- Measured intact and C-terminal FGF23 levels using ELISA in cord blood, 5-day-old infants, and adult controls.
- Utilized immunoprecipitation assays to analyze FGF23 fragmentation (32 kDa intact vs. 18 kDa fragmented).
- Statistical analysis included two-way ANOVA and Tukey's test.
Main Results:
- C-terminal FGF23 was higher in cord blood and infants than adults.
- Intact FGF23 was significantly lower in cord blood compared to infants and adults.
- Immunoprecipitation revealed abundant fragmented FGF23 (18 kDa) in cord blood, with low intact FGF23 (32 kDa).
Conclusions:
- The intact FGF23/C-terminal FGF23 ratio is markedly reduced in early postpartum infants due to FGF23 fragmentation.
- This fragmentation may play a significant role in maintaining phosphate homeostasis in healthy term infants.
Abstract:
Fibroblast growth factor 23 (FGF23) is a potent regulator of Pi and 1,25-(OH)(2)D homeostasis. Early postpartum infants show intriguing changes in serum levels of Ca, Pi, PTH and 1,25-(OH)(2)D. However, the role of FGF23 in the early neonatal mineral metabolism has not been clarified. In order to evaluate the significance of FGF23 during the early postpartum period, we examined the circulating FGF23 levels using an intact FGF23 ELISA and a C-terminal FGF23 ELISA either in 22 umbilical cord blood samples (the cord blood) or in 22 term infants at 5 days of life (the 5-day-old infant). We also compared these ranges with those of 11 healthy adults. Data were expressed as mean+/-SD, and analyzed by two-way ANOVA, followed by the Tukey's test. C-terminal FGF23 in the cord blood, the 5-day-old infants and the healthy adults were 73.3+/-22.4, 81.0+/-28.2 and 39.0+/-7.8 RU/ml, respectively. Intact FGF23 in the cord blood, the 5-day-old infants and the healthy adults were 3.9+/-1.6, 21.8+/-17.6, and 27.6+/-7.3 pg/ml, respectively. Immunoprecipitation assays using anti-FGF23 antibodies demonstrated that the intact 32 kDa FGF23 was low and the fragmented FGF23 of 18 kDa was abundant in the cord blood compared with those in the healthy adults. In conclusion, our observations indicated that the intact FGF23/C-terminal FGF23 ratio was very low due to the fragmentation of FGF23 during the early postpartum period and might have a considerable contribution to the Pi homeostasis in the healthy term infants.
